We went on Halloween last year and the costumes were awesome. In terms of crowds there were a lot of people, but getting on rides wasn't bad. Most people are there to show off their costumes so don't get on rides. Its hard for all the girls dressed as Belle to fit a full hoop skirt in ride cars! Here are a few pictures my husband took to give you an idea - Halloween 2013
Rex was hanging out near the exit of Star Tours.
Rapunzel's hair actually lit up - cool!
These girls had there photo poses down pat. The Belle is my daughter. I sewed lights into her dress as well but they are hard to see.
All the Halloween revelers hanging out to take pictures in front of the castle.
The year prior to that we went around Halloween time,but not Halloween proper. There were still a lot of costumes, but nothing like on Halloween day itself. There was a halloween scavenger hunt in TDL, but the card for it was all in Japanese. A nice cast member at the TDLH helped us translate what we couldn't and at the end of the hunt we got inflatable ghost Mickey armbands.
Our completed scavenger hunt cards! (note - their recent springtime celebration - they had a scavenger hunt card in English - yay!)
All in all, if you want to see mind blowing Disney cosplay - go to TDR at Halloween. I've done the Halloween Party at DCA which is fun and there are some great costumes, but they pale in comparison to what you see in Tokyo.